1. Field of the Invention
The invention relates in general to escalators, and more specifically to escalators of the type in which the conveyor portion is constructed of pivotally interconnected, rigid, toothed links.
2. Description of the Prior Art
A conventional step chain for an escalator driven by a large sprocket wheel normally located at the upper end of the conveyor run has several pitches between the axles to which the steps are attached. The bottom sprocket is biased to tension the chain and accommodate lengthening of the chain due to wear. If this conventional step chain wears more on one side than on the other side, there is no problems, as the chain is flexible and cannot take compressive loads.
U.S. Pat. Nos. 3,677,388; 3,682,289 and 3,707,220, which are assigned to the same assignee as the present application, disclose an escalator in which the conveyor belt is constructed of first and second loops, with each loop being constructed of pivotally interconnected rigid toothed links. Step axles join the two loops, each coaxial with a pivot axis. One or more modular drive units, located in the inclined portion of the truss, engage the toothed links on both the upper and lower runs of the conveyor to drive the conveyor in its endless loop. This will be referred to hereinafter as the modular drive chain. A significant advantage of the modular drive chain over the prior art step chain is a substantial reduction in load on the working parts, regardless of rise. The rigid links correctly space the step axles, eliminating the chain tensioning devices of the prior art.
A belt or chain constructed of pivotally interconnected rigid links, with one link between adjacent axles, can create vibration and noise when the link bushings wear. The modular chain or conveyor belt lengthens and pumps energy into the truss at the guide portions of the turn arounds, as the axle rollers transfer between the guide surfaces of the upper and lower runs. U.S. Pat. No. 4,130,192, which is assigned to the same assignee as the present application, discloses an automatic adjustment of the guide track for the axle rollers in the turnarounds. The ends of the curved guide tracks which proceed from the upper and lower runs are pivoted, and the adjacent free ends of the curved guide tracks are pivotally interconnected via a member which translates the movement of one curved guide track to the other. The arrangement requires initial adjustment of the turnarounds to the adjustment range of the cooperative guide track structure. Periodic readjustment may be required to maintain the effectiveness of the arrangement, as the link bushings wear.
If the wear of the modular drive chain should be unequal between the two sides thereof, the chain, being capable of taking compressive loads, can transmit loads into the steps during the turnarounds, which can also cause vibration, noise and undue wear.